1. Field of the Invention
The present invention relates to a piezoelectric film, a piezoelectric device using this piezoelectric film and a liquid ejection apparatus.
2. Description of the Related Art
A piezoelectric device which includes a piezoelectric body having piezoelectric characteristics whereby the body expands and contracts with increase and decrease in the intensity of an applied electric field, and electrodes through which the electric field is applied to the piezoelectric body, are used in applications such as piezoelectric actuators mounted in inkjet type recording heads. A perovskite type oxide, such as lead zirconate titanate (PZT), is used widely as piezoelectric material. The piezoelectric material is ferroelectric and possesses a spontaneous electric polarization when no electric field is applied.
It has been known since the 1960s that PZT that is doped with various donor ions having higher valence than the valence of the substituted ions has improved properties, such as ferroelectric characteristics, compared to pure PZT. Bi3+ and various lanthanide cations, such as La3+, are known as donor ions which substitute for Pb2+ at the A site. V5+, Nb5+, Ta5+, Sb5+, Mo6+, W6+, and the like, are known as donor ions which substitute for Zr4+ and/or Ti4+ at the B site.
For example, Japanese Patent Application Publication No. 2008-266772 discloses a ferroelectric film having excellent ferroelectric performance (piezoelectric performance) using a perovskite type oxide doped with 10 mol % to 40 mol % of donor ions at the B site. Japanese Patent Application Publication No. 2009-064859 discloses a ferroelectric film having excellent ferroelectric performance (piezoelectric performance), including perovskite type oxide doped with 5 mol % to 40 mol % of donor ions at the A site.
Japanese Patent Application Publication No. 2009-117592 discloses a ferroelectric film having excellent ferroelectric performance (piezoelectric performance), including perovskite type oxide doped with high-concentration donor ions at a rate of 1 mol % to 40 mol % at the A site and 10 mol % to 40 mol % at the B site. Japanese Patent Application Publication No. 2010-087144 discloses a piezoelectric film having a high piezoelectric constant when a positive voltage is applied, by limiting the amount of lead contained, the piezoelectric constant ratio, and the piezoelectric constant when a positive voltage is applied.
Japanese Patent Application Publication Nos. 2008-266772, 2009-064859 and 2009-117592 describe controlling initial characteristics by certain dopants, but include no investigation with regard to the amount of Pb and merely state that the amount of Pb may be varied within a range that yields a perovskite structure. Japanese Patent Application Publication No. 2010-087144 discloses the piezoelectric film having the improved drive durability at high humidity by reducing the amount of Pb in the film of Nb-doped PZT; however, manufacturing a film with a Pb amount of 1 or less in the ABO3 structure involves laborious operations, since the film formation conditions have to be controlled in two stages, and so on. Furthermore, if the A site is limited to Pb only, then the amount of lead is limited to not less than 0.97, and if the amount of lead is less than 0.97, then the pyrochlore phase occurs. Thus, obtaining a thin film that is a perovskite single-phase film having a small amount of Pb and that yields piezoelectric performance involves laborious manufacturing operations if the amount of lead is less than 1, and is difficult if the amount of lead is less than 0.97.